1. Field of the Invention
The present invention relates to a position detector which senses an approach or a contact of a sensing target such as a human body based on a capacitance change or the like and judges and detects the position and distance of the sensing target.
2. Description of Related Art
For example, the followings have been known as techniques for sensing an approach, etc. of a sensing target such as a human body. A light blinking device disclosed in Patent Document 1 identified below includes an electrode which senses an approach of an object, and a capacitance-type sensor which senses a change of the capacitance of the electrode. The device also includes a time selecting circuit which responds to such a change of an output from the capacitance-type sensor as has a duration of 50 milliseconds to 120 milliseconds, and a control circuit which outputs lighting and extinguishing signals based on an output from the time selecting circuit. The device further includes a switch which is opened or closed based on an output from the control circuit, and whereby the device responds to a movement of a hand of an operator.
A capacitance-type approach sensor disclosed in Patent Document 2 identified below includes a sensor unit of which capacitance changes in response to an approach of a detection object, and a sensing circuit which outputs a sensing signal that is based on the capacitance of the sensor unit. When not detecting a detection object, the sensor observes a sensing signal corresponding to a circuit-specific initial capacitance value based on a calibration instruction. A subtracting voltage generating circuit generates a subtracting voltage for offsetting this sensing signal, and a subtracting circuit outputs a calibrated sensing signal by subtracting the subtracting voltage from the sensing signal.
The following configuration can be considered in order for the capacitance-type sensors (or capacitance-based sensors) disclosed in Patent Documents 1 and 2 to improve the resolving power for position-detecting an object (a detection object). That is, as shown in FIG. 14A, a plurality of sensing electrodes 301 to 305 are arranged highly densely, and capacitance sensing circuits 311 to 315 are provided for these sensing electrodes 301 to 305 respectively. Then, as shown in FIG. 14B, in order to reduce the number of circuits, such a number of switches (mechanical relays, analog switches, photo MOS relays, etc.) SW1 to SW4 as is equal to the number of electrodes (or smaller than the number of electrodes) are provided between a plurality of sensing electrodes 301 to 304 and one capacitance sensing circuit 311. Then, measurement is carried out by scanning the capacitance sensing circuit 311 connected to the sensing electrodes 301 to 304, etc.    [Patent document 1] JPH8-64364A    [Patent Document 2] JP2006-177838A